On the Energy Efficiency of Hybrid-ARQ Protocols in Fading Channels

As the distance between terminals in modern wireless networks tends to decrease, the energy consumption issue, conventionally assumed to be exclusively dominated by the transmission power, needs to be revaluated. In particular, retransmission (ARQ) protocols that typically reduce the transmission energy required to obtain a given error probability on the channel (at the expense of a larger delay), also increase the energy consumed by the circuitry other than the power amplifier. In this paper, the energy efficiency of hybrid-ARQ type I, chase combining and incremental redundancy protocols in Rayleigh fading channels, is analyzed by accounting for the energy consumed by the transmitting and receiving electronic circuitry. It is shown that the advantages of hybrid-ARQ protocols in terms of energy consumption strictly depend on the transmission range.